This invention is directed to an expandable composition of an ethylene/higher alpha-olefin/nonconjugated diene copolymer or polychloroprene and an ionomer.
Synthetic elastomers have been expanded by the action of blowing agents to manufacture products having a cellular structure. Cellular elastomers having closed cells are especially useful because they are flexible while, at the same time, they have high compressive strengths. Such cellular products are used as automotive and constructive gaskets and pipe insulation. Although synthetic elastomers including ethylene/propylene/nonconjugated diene copolymers (EPDM) and polychloroprene can be expanded to form cellular products, it is a somewhat complicated procedure. For example, ethylene/higher alpha-olefin/nonconjugated diene copolymers have been expanded by a procedure in which the copolymer is partially cured below the decomposition temperature of the blowing agent, and then the copolymer is blown while curing is completed. Polychloroprene can be blown by a similar procedure to form closed cell expanded articles. Usually, therefore, when EPDM or polychloroprene compositions are expanded a careful balancing of compound viscoelasticity, cure rate and blowing rate is required. This necessitates the selection of a particular blowing agent and a particular curing agent so that decomposition of the blowing agent is carefully coordinated with the rate of cure of the elastomer. Accordingly, there is a need for an expandable composition of vulcanizable ethylene/higher alpha-olefin/nonconjugated diene copolymer or polychloroprene that can be easily processed and that can form a closed cell sponge having uniform cell size with little, if any, concern given to careful balancing of the cure rate with the rate of blowing.